With the depletion of natural driving forces responsible for pushing the
oil from reservoirs & declination of oil recovery after secondary stage, the emphasis is now on EOR techniques. The low saline flooding is a
type of EOR which gains the attention of
researchers due to its easiness to use implications, less cost &
environment-friendly nature. Though the low salinity effect
has been seen in various labscale core flooding experiments as well as field
pilot projects, the mechanism which actually leads to this
enhancement in recovery is still the area of research among researchers which
is wide open and needs to gain consensus. Seeing
the wide mechanisms taking place under different scenarios, it is certain that more than one mechanism is actually supplementing
each other in reducing the residual oil saturation while LSW flooding. This
study has been undertaken investigations on the low saline flooding in
unconsolidated Ottawa sandpack cores with two different, Weyburn & Pelican crude oil, to find out the optimum
salinity, LSW Slug Size & underlying mechanisms during LSW flooding.
Several core flooding experiments were performed under secondary as well as
tertiary recovery stage by unsteady state method. With the reduction of brine
salinity from 5000 PPM to 1500 PPM, the oil recovery increased
in secondary stage & decreased further upon reduction in
salinity to 500 PPM gaining the peak at 1500 PPM. Small enhancement in tertiary
recovery of 2.24% observed upon switching to 1500 NaCl PPM brine after injection
of formation brine in secondary stage for Weyburn
Oil, though large tertiary recoveries of the order of 9.95% for
effective oil viscosity of 4 cP and 7.32% for 29.7 cP were observed for n-dodecane diluted Pelican Oil.
LSW slug size of 25% pore volume was found to be effective in producing Weyburn
Oil in secondary stage.